Microwave diode switches are well-known in the art and they offer a number of advantages over mechanical switches. There are no movable contacts with the attendant problem of noise caused by poor connections and the lower switch operating speed caused by mechanical inertia. In addition, diode switches can be fabricated at a lower cost than comparable mechanical switches. Diode switches can also be packed in a smaller volume and, in particular, they are readily incorporated into transmission lines used to carry high-frequency energy.
The power that can be switched by a microwave diode switch is determined by many factors well known in the art. Several of these factors are:
(a) the frequency of the microwave energy passing through the diode (s), PA1 (b) the speed at which the diode (s) can switch between their conducting and non-conducting states, PA1 (c) the frequency at which the diode (s) are alternately switched between their conducting and non-conducting states, PA1 (d) power losses within the diode switch and the voltage standing wave ratio which is caused by impedance mismatches therein.
The power and bandwidth that can be handled by a diode microwave switch is also limited by the bias circuitry which is used to switch the diode (s) between their conducting and non-conducting states. In the prior art as the power handling capability of microwave diode switches increased, the power capabilities of the switch diode bias circuitry also had to be increased. This, in turn, increased the complexity of such control circuitry and, accordingly, increased the cost of the switches. Increasing complexity and cost of diode control bias circuitry was particularly aggravated upon the advent of microwave diode switches capable of handling one hundred or even two hundred watts of microwave frequency energy. Such a high-power microwave diode switch is disclosed in U.S. Pat. No. 3,959,750, issued May 25, 1976, to Frank Holt and assigned to the assignee of this patent.
To solve the above-described problem of costly high-power microwave switch diode control circuitry, I disclose a novel microwave switch utilizing a high-power, multi-section, hybrid coupler therein. Inputs and outputs from the microwave diode switch are connected to respective ones of the legs of the hybrid coupler. In addition, the switch control circuit is connected to another leg of the hybrid coupler. The leg to which the switch control circuit is connected and any remaining legs of the hybrid coupler are all capacitively grounded to provide a d-c open circuit to diode switching potentials while providing a short circuit to RF signals within the switch. This causes RF signals in these capacitively ground coupler legs to be reflected back into the switch in a manner well known in the art. The result of utilizing a hybrid coupler is that the hybrid leg to which the bias circuit is connected is only exposed to a portion of the microwave frequency energy input to the switch thereby providing isolation, and a relatively low power bias circuit may thereby be used to control the operation of the diode switch. This feature increases the RF bandwidth of said switching device.